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UNIVERSITY  OF  ILLINOIS 

Agricultural  Experiment  Station 


BULLETIN  No.  218 


THE  PRUNING  OF  WINTER-INJURED 
PEACH  TREES 


BY  A.  J.  GUNDEBSON 


SUMMARY  OF  BULLETIN  No.  218 

INTRODUCTION. — Unusually  low  temperatures  of  the  winter  of  1917-18  caused 
serious  injury  to  peach  trees  in  southern  Illinois,  and  peach  growers  were  at 
a  loss  to  know  how .  their  trees  should  be  treated,  especially  with  reference  to 
pruning.  Page  383 

EFFECTS  OF  WINTER  INJURY. — Trees  which  had  been  planted  one  year  showed 
less  injury  than  older  trees.  The  injury  included  the  killing  of  fruit  buds  and 
injury  to  trunks  and  branches.  Little  root  injury  was  observed.  Discoloration 
of  the  inner  wood  varying  from  light  to  dark  brown  was  the  principal  internal 
symptom.  Page  383 

FACTORS  AFFECTING  SEVERITY  OF  INJURY. — Trees  devitalized  by  borers,  gum- 
mosis,  and  starvation  suffered  serious  winter  injury.  Those  located  in  the  lower 
parts  of  the  orchards  showed  more  injury  than  those  on  higher  parts.  Page  385 

VARIETIES  INJURED. — Observations  of  Hale  trees  showed  more  serious  wood 
injury  among  them  than  among  Elbertas.  Page  385 

EXPERIMENTAL  PROJECT. — Experimental  work  was  confined  to  Elbertas.  On 
three-,  four-,  and  five-year-old  trees,  moderate  pruning  gave  the  best  results 
from  the  standpoint  of  size,  shape,  and  openness  of  the  trees  and  in  the  number 
of  vigorous  fruit  buds  formed  on  strong  wood.  Dehorning  trees  of  these  ages 
proved  a  poor  practice.  It  reduced  the  size  of  the  trees  and  in  the  case  of  the 
five-year-old  Elbertas  in  the  Voris  orchard,  killed  the  trees.  No  pruning  at 
all  gave  better  results  than  the  dehorning  of  three-,  four-,  and  five-year-old 
Elbertas.  Waxing  the  cut  surface  of  dehorned  trees  was  of  no  value.  Nitrate 
of  soda  applied  at  the  rate  of  one  pound  per  tree  increased  the  amount  and  color 
of  the  foliage  on  moderately  pruned  four-year-old  Elbertas  and  on  check  trees,  but 
was  of  little  value  on  dehorned  trees  of  this  age  and  variety.  Page  386 

Discoloration  of  the  inner  wood  is  not  an  absolute  indication  of  the  inability 
of  trees  to  recover  from  the  effects  of  winter  injury.  In  the  orchards  studied, 
in  most  cases  in  which  discoloration  had  resulted  from  the  winter  injury  of  1917-18, 
new  sapwood  was  observed  the  following  November.  The  heartwood  and  pith  of 
trunks  and  branches  showed  a  ' '  punky ' '  or  decomposed  condition.  Page  394 


THE  PRUNING  OF  WINTER-INJURED 
PEACH  TREES 

BY  A.  J.  GUNDEKSON,  ASSOCIATE  IN  HORTICULTURE 

INTRODUCTION 

Unusual  and  prolonged  periods  of  low  temperature  in  southern 
Illinois  during  the  winter  of  1917-18  resulted  in  serious  injury  to 
peach  trees.  The  month  of  December,  1917,  was  the  most  severe 
month  in  the  climatological  history  of  the  state.  In  many  peach- 
growing  localities  of  southern  Illinois  the  temperature  reached  as  low 
as  -20°  and  -25°  Fahrenheit.  During  the  periods  of  low  temperature 
strong  winds  prevailed.  Fortunately,  however,  there  was  a  good  cov- 
ering of  snow  in  most  peach  orchards,  and  therefore  the  injury  was 
confined  to  the  trunks  and  the  branches  of  the  trees. 

Peach  growers  were  at  a  loss  to  know  how  their  trees  should  be 
treated,  especially  with  reference  to  pruning.  Some  were  pruning 
their  trees  severely,  while  others  were  pruning  moderately.  The  writer 
recommended  moderate  pruning  for  both  old  and  young  peach  trees, 
as  experimental  evidence  had  indicated  that  for  winter-injured  peach 
trees  more  than  one  year  old  moderate  pruning  was  better  than  severe 
pruning.1  In  the  case  of  June-budded  or  small  yearling  trees  planted 
during  the  fall  of  1917,  however,  it  was  recommended  that  the  usual 
cutting  back  to  whips  be  practiced. 

EFFECTS  OF  WINTER  INJURY 

Winter  injury  to  peach  trees  in  Illinois  during  the  winter  of 
1917-18  included  the  killing  of  the  fruit  buds  and  injury  to  wood  of 
different  ages,  varying  from  a  slight  injury  to  the  tissues  to  severe 
injury  and  subsequent  death  of  the  trees.  In  most  cases  trees  which 
had  been  planted  but  one  year  showed  less  injury  than  older  trees. 

INTERNAL  SYMPTOMS  OF  WINTER  INJURY 

The  internal  symptoms  of  winter  injury  appeared  in  the  form  of 
discoloration  of  the  heartwood  and  sapwood,  varying  in  color  from 
light  to  dark  brown  (Figs.  1  and  2) .  The  cambium  layer  turned  a  pale, 
watery  green.  The  odor  of  the  cell  sap  was  sour,  suggesting  f  ermenta- 


'Mass.   (Hatch)  Agr.  Exp.  Sta.  Ept.  1905,  p.  167. 
U.  S.  Dept.  Agr.  Bur.  Plant  Indus.  Bui.  51,  part  III. 
N.  Y.   (Geneva)   Agr.  Exp.  Sta.  Bui.  269. 

383 


384 


BULLETIN  No.  218 


[May, 


tion.  These  conditions  were  present  in  the  trunk  and  the  branches. 
The  roots  of  the  trees  in  every  peach  orchard  examined  remained 
normal,  owing  to  the  protection  afforded  by  the  heavy  covering  of 
snow  (Fig.  3). 


FIG.  1. — LONGITUDINAL  SECTION  OF  BRANCH  AND  TRUNK  OF  FIVE-YEAR-OLD 

ELBERTA 

Note  the  discoloration  of  the  wood   of  the  trunk   in  comparison  with  the 
healthy  uninjured  wood  of  the  small  branch  at  the  right. 


FIG.  2. — CROSS-SECTION  OF  BRANCH  AND  TRUNK  OF  FIVE-YEAR-OLD  ELBERTA 

Note  the  discoloration  of  the  wood  of  the  trunk  in  comparison  with  the 
healthy,  uninjured  wood  of  the  small  branch  at  the  right. 


1919} 


PRUNING  OF  WINTER-INJURED  PEACH  TREES 


385 


EXTERNAL  SYMPTOMS  OF  WINTER  INJURY 

The  first  external  symptoms  of  winter  injury  appeared  in  the 
form  of  shrunken  bark  on  which  the  lenticles  stood  out  prominently, 
giving  the  bark  a  slightly  roughened  appearance;  and  also  in  some 
cracking  or  splitting  of  the  tree  trunks.  A  later  symptom  was  noted 
in  which  the  leaf  buds  expanded,  owing  to  the  local  supply  of  stored 
food,  but  finally  wilted  on  account  of  the  inability  of  the  injured  tis- 
sues to  conduct  sap  from  the  roots.  This  type  of  injury  appeared 
both  on  single  branches  and  on  entire  trees. 

FACTORS  AFFECTING  SEVERITY  OF  INJURY 

The  amount  of  winter  injury  to  peach  orchards  in  southern  Illi- 
nois varied  not  so  much  with  latitude,  for  the  low  temperatures  were 
quite  uniform,  as  with  differences  in  vigor  and  healthiness  of  the  trees, 
elevation  of  the  orchard,  and  age  of  the  trees.  Trees  devitalized  as 
the  result  of  previous  injury  from  borers,  gummosis,  and  lack  of 
proper  feeding  and  cultiva- 
tion were  most  severely  in- 
jured and  in  many  cases  died. 
Those  located  on  well  elevated 
and  properly  drained  soil 
showed  less  serious  injury 
than  those  situated  on  level 
land  or  in  "pockets."  In 
some  cases  a  difference  of  a 
few  feet  in  elevation  within 
the  same  orchard  caused  a 
marked  difference  in  the  se- 
verity of  the  injury.  Trees 
which  had  been  planted  one 
year  appeared  to  be  injured 
less  than  older  trees. 


Little  opportunity  was  af- 
forded to  study  winter  injury 
on  any  variety  of  peach  trees 
other  than  Elberta  and  Hale. 
The  former  variety  is  the 
most  important  one  grown 
commercially  in  southern  Illi- 
nois, while  the  latter  is  being 
planted  to  some  extent.  It 


FIG,  3. — HORIZONTAL  SECTION  OF  ELBERTA 

TREE 

Note  the  discoloration  of  wood  beginning 
at  the  snow-line  (X)  as  compared  with  the 
uninjured  wood  at  Y,  below  the  snow-line. 


386  BULLETIN  No.  218  [May, 

has  been  thought  by  certain  peach  growers  of  other  states  that  Hale 
is  more  resistant  to  low  temperatures  in  the  bud  than  is  Elberta,  but 
in  southern  Illinois,  during  the  winter  of  1917-18,  both  varieties 
proved  failures  in  this  particular.  Hale  is  a  less  thrifty  grower  than 
is  Elberta  in  this  section  of  the  state  and  following  the  winter  of 
1917-18  showed  as  much,  and  in  certain  cases  more,  serious  wood 
injury. 

EXPERIMENTAL  PROJECTS 

As  serious  winter  injury  to  the  wood  of  peach  trees  rarely  occurs 
in  southern  Illinois,  advantage  was  taken  of  the  opportunity  offered 
at  this  time  to  conduct  investigations  with  the  view  of  determining  a 
satisfactory  way  of  handling  such  trees.  Experimental  work  was  con- 
fined to  the  Elberta  variety. 

VORIS  ORCHARD,  NEOGA,  CUMBERLAND  COUNTY 

In  the  spring  of  1918,  the  entire  Voris  peach  orchard  at  Neoga 
showed  serious  winter  injury,  with  some  dead  trees  in  the  lowest 
parts.  The  trees  were  five-year-old  Elbertas  which  had,  up  to  that 
time,  received  fairly  good  care.  They  stood  on  level  to  undulating 
gray  silt  loam  soil. 

Four  rows  of  trees  containing  seven  in  each  row  were  selected 
and  pruned  as  follows  on  March  28,  when  the  leaf  buds  had  started : 

Row  1.     One-half  of  the  previous  year's  wood  was  removed. 

Bow  2.  Dehorned  to  within  eighteen  inches  to  two  feet  of  the  trunks,  the 
one-,  two-,  and  three-year-old  wood  being  removed.  Three  trees 
were  waxed  at  the  cut  surfaces  and  four  left  unwaxed. 

Row  3.     Check.     Unpruned. 

Row  4.  From  four  trees  all  the  previous  year's  wood  was  removed.  Three 
trees  were  pruned  leaving  four  inches  of  the  previous  year 's  wood. 

Judging  from  the  discoloration  of  the  wood  of  all  the  trees  in 
this  experiment,  the  injury  was  very  severe.  In  Row  2  the  wounds 
of  three  of  the  trees  were  waxed  immediately  after  dehorning,  while 
four  trees  were  left  unwaxed  with  the  view  of  determining  whether 
or  not  the  checking  of  evaporation  would  aid  recovery. 

On  July  23,  observations  were  made  upon  the  relative  condition 
of  the  trees.  The  trees  in  Rows  1  and  4  were  the  best  from  the  stand- 
point of  growth  and  amount  and  color  of  the  foliage.  The  check  or 
unpruned  trees  were  making  a  straggling  growth  and  presented  an 
unthrifty  appearance.  All  the  trees  in  Row  2,  which  had  been  de- 
horned, were  practically  dead,  with  the  exception  of  one  unwaxed  tree. 
It  may  be  concluded,  therefore,  that  evaporation  at  the  cut  surfaces 
of  the  dehorned  trees  was  not  directly  responsible  for  their  death. 
The  dehorning  of  these  trees  resulted  in  an  extreme  reduction  in  the 
amount  of  leaf  surface  with  a  corresponding  reduction  in  amount  of 
transpiration.  As  it  is  quite  probable  that  transpiration  in  peach  trees 


1919]  PRUNING  OF  WINTER-INJURED  PEACH  TREES  387 

exerts  some  effect  upon  the  flow  of  sap,  it  seems  likely  that  the  trees 
of  Row  2  did  not  draw  a  sufficient  amount  of  sap  from  their  roots  to 
sustain  them  and  permit  growth.  Then,  too,  the  season  was  extremely 
hot  and  dry. 

On  October  29,  observations  were  again  made  to  ascertain  the  con- 
dition of  the  trees  in  the  different  rows.  In  Row  2  only  one  tree  re- 
mained alive,  one  which  had  been  left  unwaxed.  It  had  made  the 
usual  heavy  growth  characteristic  of  dehorned  peach  trees  and  carried 
practically  no  fruit  buds.  The  trees  in  Rows  1  and  4  had  an  abun- 
dance of  fruit  buds  present  on  strong  wood.  The  unpruned  trees  in 
Row  3  showed  plenty  of  fruit  buds,  but  they  were  borne  on  small, 
weak  branches. 

POFF  ORCHARD,  OLNEY,  RICHLAND  COUNTY 

The  Poff  peach  orchard  at  Olney  showed  a  variable  degree  of 
winter  injury  following  the  winter  of  1917-18.  That  part  of  the 
orchard  well  elevated  and  properly  drained  consisted  of  four-year-old 
Elbertas.  The  rest  of  the  trees,  situated  on  more  level  and  lower 
ground,  were  three-year-old  Elbertas,  which  seemed  to  show  slightly 
more  serious  injury  than  the  four-year-old  trees  on  the  higher  ground. 
The  soil  of  this  orchard  is  yellow  gray  silt  loam. 

Series  1:  Three-Y  ear-Old  Elbertas 

Four  rows  containing  five  three-year-old  Elberta  trees  each  were 
pruned  in  the  following  manner  on  March  26,  when  the  leaf  buds 
were  out: 

Kow  1.     Pruned  moderately;  previous  year's  growth  clipped  approximately 

one-half. 

Row  2.     Dehorned,  the  one-  and  two-year-old  wood  removed. 
Eow  3.     One-year-old  wood  removed. 
Row  4.     Check.    Unpruned. 

On  May  12,  the  trees  of  Rows  1  and  3  were  making  the  best 
growth  and  carrying  the  best  colored  foliage.  The  trees  in  Row  2, 
which  had  been  dehorned,  were  growing  slowly  .but  had  good  foliage. 
The  unpruned  trees  were  making  the  poorest  growth  and  carried 
sickly,  yellow  leaves. 

On  July  9,  the  trees  in  Row  3,  from  which  all  of  the  previous 
year's  wood  had  been  removed,  had  made  the  greatest  amount  of 
growth,  while  the  trees  in  Row  1,  the  one-year-old  wood  of  which  had 
been  clipped,  were  second,  with  the  trees  in  Row  2,  which  had  been 
dehorned,  and  those  of  Row  4,  which  had  been  left  unpruned,  fol- 
lowing in  amount  of  growth.  Trees  which  had  been  dehorned  were 
very  dense  and  were  reduced  so  low  that  much  of  the  growth  lay  on 
the  ground,  and  was  therefore  useless  so  far  as  its  ability  to  carry 


BULLETIN  No.  218 


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PRUNING  OP  WINTER-INJURED  PEACH  TREES 


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390  BULLETIN  No.  218  [May, 

fruit-bearing  wood  in  the  future  was  concerned.  In  Figs.  4  to  7  one 
tree  from  each  of  the  four  rows  is  shown. 

On  October  30,  when  most  of  the  leaves  had  fallen,  observations 
were  made  to  determine  the  relative  amounts  of  fruit-bud  formation 
on  the  trees  of  the  different  rows.  The  greatest  number  of  fruit  buds 
had  developed  in  Row  1,  the  trees  whose  one-year-old  wood  had 
been  clipped;  the  next  greatest  number  was  on  the  trees  in  Row  4, 
which  had  not  been  pruned,  while  a  smaller  number  of  buds  was 
present  on  the  trees  in  Row  3,  from  which  the  one-year-old  wood  had 
been  removed.  Row  2,  the  trees  of  which  had  been  dehorned,  de- 
veloped practically  no  fruit  buds,  owing  to  the  very  heavy  primary 
growth  that  resulted  from  the  severe  pruning. 

The  fruit  buds  on  the  trees  of  Rows  1  and  3,  which  had  been 
moderately  pruned,  were  carried  on  strong  growth,  while  those  on 
the  unpruned  trees  in  Row  4  developed  on  small,  weak  branches. 

Series  2:  Four-Y  ear-Old  Elbertas 

Five  rows  of  trees,  each  containing  five  four-year-old  Elbertas, 
were  pruned  in  the  following  manner  on  March  26,  when  the  leaf  buds 
were  out: 

Kow  1.     Pruned  moderately,  previous  year's  growth  clipped  approximately 

one-half. 

Bow  2.     Dehorned,  the  one-,  two-,  and  three-year-old  wood  removed. 
Kow  3.    One-year-old  wood  removed. 

Eow  4.     Dehorned,  the  one-  and  two-year-old  wood  removed. 
Eow  5.    Check.    Unpruned. 

On  April  1,  one  pound  of  nitrate  of  soda  was  applied  broadcast 
to  threa  trees  in  each  row  for  the  purpose  of  studying  the  effects  of 
this  fertilizer  on  the  recovery  of  the  trees  from  winter  injury. 

On  May  12,  the  trees  in  Rows  1  and  3  were  making  a  better  type 
of  growth  than  those  in  Rows  2  and  4.  The  unpruned  trees  in  Row  5 
were  making  weaker  growth  at  this  time. 

The  foliage  of  the  trees  which  had  received  the  nitrate  of  soda 
was  heavier  and  of  a  darker  green  color  than  that  of  the  untreated 
trees.  This  difference  was  much  more  apparent,  however,  in  the  check 
and  the  moderately  pruned  trees  than  in  those  dehorned.  This  was 
probably  due  to  the  fact  that  heavy  pruning  of  peach  trees  usually 
results  of  itself  in  the  stimulation  of  a  heavy  growth  of  wood  and 
foliage,  especially  when  the  trees  are  in  vigorous  condition. 

On  July  9,  the  rankest  growth  had  been  made  by  the  trees  in 
Rows  2  and  4.  The  tops  were  very  dense  and  were  reduced  so  low  that 
many  of  the  branches  lay  on  the  ground,  making  it  necessary  to  re- 
move them  later.  The  trees  which  were. making  the  most  desirable 
growth  from  the  standpoint  of  amount  and  spread  were  those  in  Row 


1919] 


PRUNING  OF  WINTER-INJURED  PEACH  TREES 


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PRUNING  OF  WINTER-INJURED  PEACH  TREES 


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FIG.  12. — SERIES  2,  Eow  5:   FOUR- YEAR-OLD  ELBERTA 
Check.     Unpruned. 

1,  whose  one-year-old  wood  had  been  clipped  one  half.  The  next  best 
trees  were  those  in  Row  3,  from  which  the  one-year-old  wood  had  been 
entirely  removed.  The  unpruned  trees  were  better  than  those  de- 
horned, from  the  standpoint  of  both  size  and  shape. 

The  effects  of  the  nitrate  of  soda  were  still  noticeable  on  the 
check  trees  and  on  the  trees  which  had  been  moderately  pruned. 

Observations  were  made  October  30  on  the  relative  amount  of 
fruit-bud  formation  on  the  trees  in  the  different  rows.  The  trees  in 
Eow  1,  whose  one-year-old  wood  had  been  clipped,  carried  the 
largest  number  of  well  distributed,  vigorous  fruit  buds  and  on 
wood  of  desirable  size.  The  unpruned  trees  carried  a  large  number 
of  less  plump  but  well  distributed  fruit  buds  on  small-sized  branches. 
The  trees  in  Row  3,  from  which  the  one-year-old  wood  had  been  re- 
moved entirely,  had  a  good  many  poorly  distributed  fruit  buds  car- 
ried on  wood  that  was  a  little  too  heavy  to  be  desirable.  The  tops 
of  the  trees  in  this  row  were  so  dense  as  to  require  considerable  thin- 
ning of  the  branches  and  consequent  removal  of  many  fruit  buds. 

Very  few  fruit  buds  were  present  on  the  dehorned  trees  in  Rows 
2  and  4.  This  was  due  to  the  fact  that,  as  usual  on  severely  pruned 
trees,  long  and  heavy  primary  growth  of  branches  developed,  on  which 
relatively  few  fruit  buds  ever  appear. 


394 


BULLETIN  No.  218 


INTERNAL  APPEARANCE  OF  WOOD  TISSUES  AT  THE 
END  OF  THE  GROWING  SEASON 

Examination  of  the  internal  tissues  of  the  wood  of  both  branches 
and  trunks  was  made  in  both  experimental  orchards  during  November 
after  the  growing  season  had  ended.  It  was  observed  that  a  new  layer 
of  sap  wood  had  been  formed,  of  greater  thickness  in  the  trunks  of 
the  trees  than  in  the  branches  (Fig.  13).  The  heartwood  and  pith 
had  assumed  a  "punky"  condition,  suggesting  decomposition. 
Whether  such  a  condition  will  eventually  prove  detrimental  to  the 
productiveness  and  vigor  of  the  trees  remains  to  be  seen. 


FIG.  13. — CROSS-SECTION  OP  BRANCH  AND  TRUNK  OF  THREE- YEAR-OLD  ELBERTA 

MADE  ON  NOVEMBER  15,  1918 

Note  the  "punky"  condition  of  the  pith  and  heartwood;    also  the  new  ring 
of  sapwood  formed  around  the  injured  tissues. 


UNIVERSITY  OF  ILLINOIS-URBANA 


